User's Manual

Intel
®
820 Chipset Design Guide 3-5
Advanced System Bus Design
3.2.1 Initial Timing Analysis
Perform an initial timing analysis of the system using Equation 3-1 and Equation 3-2 shown below.
These equations are the basis for timing analysis. To complete the initial timing analysis, values for
clock skew and clock jitter are needed, along with the component specifications. These equations
contain a multi-bit adjustment factor, M
ADJ
, to account for multi-bit switching effects such as SSO
pushout or pull-in that are often hard to simulate. These equations do not take into consideration all
signal integrity factors that affect timing. Additional timing margin should be budgeted to allow for
these sources of noise.
Equation 3-1. Setup Time
T
CO_MAX
+ T
SU_MIN
+ CLK
SKEW
+ CLK
JITTER
+ T
FLT_MAX
+ M
ADJ
≤ Clock Period
Equation 3-2. Hold Time
T
CO_MIN
+ T
FLT_MIN
-
M
ADJ
≥ T
HOLD
+ CLK
SKEW
Symbols used in Equation 3-1 and Equation 3-2:
—T
CO_MAX
is the maximum clock to output specification
1
.
—T
SU_MIN
is the minimum required time specified to setup before the clock
1
.
—CLK
JITTER
is the maximum clock edge-to-edge variation.
—CLK
SKEW
is the maximum variation between components receiving the same clock edge.
—T
FLT_MAX
is the maximum flight time as defined in Section 3.1, “Terminology and
Definitions” on page 3-1.
—T
FLT_MIN
is the minimum flight time as defined in Section 3.1, “Terminology and
Definitions” on page 3-1.
—M
ADJ
is the multi-bit adjustment factor to account for SSO pushout or pull-in.
—T
CO_MIN
is the minimum clock to output specification
1
.
—T
HOLD
is the minimum specified input hold time.
Note: The Clock to Output (T
CO
) and Setup to Clock (T
SU
) timings are both measured from the signals
last crossing of V
REF
, with the requirement that the signal does not violate the ringback or edge
rate limits. See the respective Processor’s datasheet and thePentium® III Processor Developer’s
Manual for more details.
Solving these equations for T
FLT
results in the following equations:
Equation 3-3. Maximum Flight Time
T
FLT_MAX
≤ Clock Period - T
CO_MAX
- T
SU_MIN
- CLK
SKEW
- CLK
JITTER
- M
ADJ
Equation 3-4. Minimum Flight Time
T
FLT_MIN
≥ T
HOLD
+ CLK
SKEW
- T
CO_MIN
+ M
ADJ